Mount for use in optical fiber hydrophone array

ABSTRACT

A mount for use in an optical fiber hydrophone module to loosely secure hydrophone components while avoiding increasing noise to the hydrophone. A hydrophone core has a plurality of mandrels helically wrapped with optical fiber and connected along an axis. A cylindrical metal cage encircles the hydrophone core. Cloth tape is wrapped around and affixed to the metal cage. An open pore foam goes around the metal cage. Thermoplastic adhesive attaches the foam to the cloth tape. A cylindrical woven internal strength member goes around the foam, including two longitudinal positioning tapes. The positioning tapes are fastened to the member at each end, and the foam is between the positioning tapes. Thread is used to sew the positioning tapes to the foam at spaced intervals along the axis.

FEDERAL RESEARCH STATEMENT

This invention was made with Government support under ContractN00024-98-C-6308. The Government has certain rights in this invention.

BACKGROUND OF INVENTION

The science of underwater sonar equipment is increasingly relying on theuse of fiber-optic technology. This reliance is driven by therequirement to have more acoustic sensors per sonar system, with highersensitivities and lower cost.

Passive sonar arrays towed from submarines or surface ships areexcellent candidates for fiber-optic sensor technology. In this area, anall optical fiber hydrophone assembly is a recent development by theUnited States Naval Research Laboratories. The hydrophone assemblyconsists of a series of air-backed plastic cylinders, called mandrels,which are helically wrapped with optical sensing fiber. The hydrophonesenses sound pressure levels through the strain induced in the opticalsensing fiber as the sound pressure wave deforms the mandrel. Strain isimparted in the fiber in direct proportion to the pressure inducedstrain in the mandrel. The characteristics of the light signaltransmitted through the fiber change in relation to the strain in thefiber, allowing measurement of the sound pressure level based on thechange in the light signal. The mandrels are interconnected by axialinterconnect springs to form a line of mandrels that make up thehydrophone assembly. The hydrophone assembly is integrated into adiscrete thin-line acoustic module. Modules typically range from 50 to250 feet in length. End-to-end connection of modules forms long opticalhydrophone sonar arrays. Bulkhead couplings are located at each end ofthe modules and provide connections between adjacent modules. The activesensing hydrophone fiber must transition into and through the modulecouplings. This requires the interconnection of optical fibers.

While large bandwidth capabilities and small size make optical fibersdesirable for use, optical fibers are mechanically fragile. Tow-inducedloads may cause the fibers to fracture. Such loads may be induced indeployment and recovery operations of the acoustic array, in towing ofthe acoustic array by drag loading induced elongation, and in bending ofthe optical fiber. The optical fiber is bent when the optical hydrophonesonar array is wound on a handling system reel. Radial compressive loadsmay cause degraded light transmission as the result of a phenomenonknown as microbending loss. Stress corrosion is another cause of failureof optical fibers, and is a stress-accelerated chemical reaction betweenthe optical fiber glass and water that can result in microcracks in theglass, adversely effecting fiber performance.

To accommodate desired growth in the field of optical fiber hydrophones,it is necessary that new apparatus and methods for use with opticalhydrophone sensor technology be developed to protect the fibers frommechanical failure. For example, while the optical fiber is relativelywell protected while wound on the hydrophone mandrels and interconnectsprings, there is a need for a reliable means of transitioning opticalfibers on and off the optical hydrophone assembly in the critical areasat each end of the module where the fiber transitions to the bulkheadcoupling. There is also a need for protecting the optical fibers as theymake the transition from the optical hydrophone sensors tooptical-mechanical terminations that provide interconnectivity throughthe bulkheads to other towed sonar array modules.

Optical fibers serving individual modules are limited in the number oflight transmission channels available for communication with themonitoring equipment in the vessel. Multiple optical fibers maytherefore be required to service an entire hydrophone array. Thesebypass fibers are needed in order to serve aft modules in the hydrophonearray. Optical fibers that service modules aft of the forward modulemust bypass the hydrophone assembly of one or more modules by a routeoutside of the hydrophone assembly, creating the need for protection ofthe bypass fibers. The bypass fibers are aligned with the module centralaxis proximate to each end of the module. The bypass fibers transitionto be substantially parallel to the module central axis and alongsidethe hydrophone assembly. Bypass fibers must be protected from strainresulting from tow speed induced-drag loading. Reliable end terminationsare also required.

Modules require a fill fluid in order to have neutral buoyancy. Meansfor filling the module that provide a seal for both the module and forthe fiber that passes through the module seal are needed. There is alsoa need for improvement in the physical connections between the opticalfibers of adjacent modules. Existing optical towed sonar arrays usevarious configurations of standard optical connector technologies.Specially designed optical-mechanical connectors are available, butrequire large physical space envelopes, both in diameter and length.Such connectors include fiber splice trays, which are commerciallyavailable, but are too large for retrofitting into thin-line towed sonararrays.

A general splicing technique with proven reliability is also needed.Fiber splicing is a necessary step in integrating prefabricatedsubcomponents of hydrophone assemblies into the towed array opticalmodule assembly. The optical fiber end terminations should be fabricatedoff-line, eliminating the need, and the risk of damage, for integratingthe active sensing fiber into the end termination components. Thesplicing apparatus should also be effective in repairing an opticalfiber break during the hydrophone winding process during fabrication ofthe optical hydrophone assembly.

SUMMARY OF INVENTION

The present invention is for use in an optical hydrophone module, andmore specifically, between the ends of modules. An optical hydrophonemount according to the present invention provides a structure that helpsto avoid imparting or contributing to increased noise levels fromcomponents that surround and secure the hydrophone.

A mount having features according to the present invention may be usedin an optical fiber hydrophone module. The module comprises a generallycylindrical optical hydrophone core and has a plurality of mandrelshelically wrapped with optical fiber and connected in linear relationwith interconnect springs. A cylindrical metal cage encircles thehydrophone core, circumferentially abutting the interconnect springs,and may have pairs of longitudinal slots spaced along the axis. A clothtape is wrapped around and affixed to the metal cage. An open pore foamencircles and circumferentially abuts the metal cage. Means forattaching the foam to the cloth tape are provided. An internal strengthmember encircles the foam, comprising a hollow woven cylinder that mayinclude aramid fibers and one or more longitudinal positioning tapesinside of and extending for the full length of the cylinder. Thepositioning tapes are fastened to the cylinder at each end, and the foamis between the positioning tapes. Means are providing for fastening thepositioning tapes to the foam at spaced intervals along the axis.

In further embodiments of the present invention, the metal cage issteel, the cloth tape is woven polyester, the open pore foam ispolyurethane, means for attaching the foam to the cloth tape isthermoplastic adhesive, the internal strength member comprises aramidfibers, and the means for fastening the positioning tapes to the foamcomprises thread. A hydrophone module having various elements of theabove invention is also provided.

In addition, a method of mounting a hydrophone is provided. The stepsinclude placing a cylindrical metal cage around the hydrophone core sothat the cage circumferentially abuts the interconnect springs. A clothtape is wrapped around and affixed to the metal cage. An open pore foamis placed around and circumferentially abuts the metal cage. The foam isattached to the cloth tape, and an internal strength member is placedaround the foam. Positioning tapes are tensioned and then are fastenedto the foam at paced intervals along the hydrophone axis.

Features and advantages of the present invention will become moreapparent in light of the following detailed description of some of theembodiments thereof, as illustrated in the accompanying figures. As willbe realized, the invention is capable of modifications in variousrespects, all without departing from the invention. Accordingly, thedrawings and the description are to be regarded as illustrative innature, and not as restrictive.

BRIEF DESCRIPTION OF DRAWINGS

For a more complete understanding of this invention reference should nowbe had to the embodiments illustrated in greater detail in theaccompanying drawings and described below.

FIG. 1 is an elevation view of a submarine towing a hydrophone array.

FIG. 2 is a plan view of a hydrophone module with some elements cutaway, illustrating some of the elements of the present invention.

FIG. 3 is a perspective view of a hydrophone segment.

FIG. 4 is a perspective view of an interconnect spring used in thehydrophone segment of FIG. 3.

FIG. 5 is a longitudinal section view of the hydrophone module takenalong line 55 of FIG. 2.

FIG. 6 is a cross-section view of the hydrophone module taken along line66 of FIG. 2.

FIG. 7 is a perspective view of the woven fiber protection cableassembly, fiber transition segment, and hydrophone assembly used in theembodiment of FIG. 2.

FIG. 8 is a perspective view of a woven fiber protection cable assemblyof the present invention used in the embodiment of FIG. 2.

FIG. 9 is a plan view of the woven fiber protection cable assembly ofFIG. 8.

FIG. 10 is an elevation view of the woven fiber protection cableassembly of FIG. 8.

FIG. 11 is a perspective view of a fiber transition segment of thepresent invention, used in the embodiment of FIG. 2.

FIG. 12 is a section view taken along the longitudinal axis of the fibertransition segment of FIG. 11.

FIG. 13 is a perspective view of a fiber bypass assembly of the presentinvention.

FIG. 14 is an enlarged perspective view of the embodiment of FIG. 13.

FIG. 15 is an exploded perspective view of one end of the embodiment ofFIG. 2.

FIG. 16 is section view used in the description of a bulkhead coupling,fiber splice tray, termination assembly, and clevis of FIG. 15.

FIG. 17 is a perspective view of a termination assembly of theembodiment of FIG. 15.

FIG. 18 is an enlarged exploded perspective view of an optical fiberseal of the embodiment of FIG. 15.

FIG. 19 is a perspective view of a fiber seal retainer of the embodimentof FIGS. 18.

FIG. 20 is a longitudinal section view of the fiber seal retainer ofFIG. 19.

FIG. 21 is a perspective view of the fiber seal of the embodiment ofFIG. 18.

FIG. 22 is a longitudinal section view of the fiber seal of FIG. 21.

FIG. 23 is a perspective view of a compressive tube stop of theembodiment of FIGS. 17 and 18.

FIG. 24 is a longitudinal section view of the compressive tube stop ofthe embodiment of FIG. 23.

FIG. 25 is a longitudinal section view of an end cap of the embodimentof FIG. 18.

FIG. 26 is a perspective view of the fiber-optic splice tray of theembodiment of FIG. 15.

FIG. 27 is another perspective view of the fiber-optic splice tray ofthe embodiment of FIG. 15.

FIG. 28 is a cross-section view of the fiber-optic splice tray takenalong line 2828 of FIG. 27.

FIG. 29 is another cross-section view of the fiber-optic splice traytaken along line 2929 of FIG. 27.

FIG. 30 is a perspective view of another embodiment of the fiber-opticsplice tray of FIG. 15.

FIG. 31 is a partially exploded perspective view of an optical fibersplicing apparatus of the present invention and a hydrophone mandrel.

FIG. 32 is a perspective view of the optical fiber splicing apparatus ofFIG. 31, installed on a hydrophone mandrel.

FIG. 33 is a plan view of the splice protector of the optical fibersplicing apparatus of FIG. 31.

FIG. 34 is a longitudinal section view of the splice protector takenalong line 3434 of FIG. 33.

FIG. 35 is a cross-section view of the splice protector taken along line3535 of FIG. 33.

FIG. 36 is a plan view of a rotation sleeve of the optical fibersplicing apparatus of FIG. 31.

FIG. 37 is a longitudinal section view of the rotation sleeve takenalong line 3737 of FIG. 36.

FIG. 38 is a cross-section view of the rotation sleeve taken along line3838 of FIG. 36.

FIG. 39 is a partial longitudinal section view of the fastening of opencell foam to a positioning tape of the embodiment of the presentinvention in FIG. 2.

FIG. 40 is a partial longitudinal section of the fastening of a bypasscable assembly to a positioning tape of the embodiment of the presentinvention in FIG. 2.

FIG. 41 is an elevation view of a hydrophone assembly of the presentinvention.

FIG. 42 is an exploded perspective view of a hose pulling assembly usedto assemble the embodiment of FIG. 2.

FIG. 43 is a perspective view of a hose pulling assembly used toassemble the embodiment of FIG. 2.

DETAILED DESCRIPTION

Certain terminology is used herein for convenience only and is not to betaken as a limitation on the invention. For example, words such asforward, aft, upper, lower, left, right, horizontal, vertical, upward,and downward merely describe the configuration shown in the Figures. Thecomponents may be oriented in any direction and the terminology,therefore, should be understood as encompassing such variations unlessspecified otherwise. Also, the scope of the invention is not intended tobe limited by the materials or dimensions listed herein, but may becarried out using any materials and dimensions that allow theconstruction and operation of the hydrophone module.

Referring now to the drawings, wherein like reference numeralsillustrate corresponding or similar elements throughout the severalviews, there is shown in FIG. 1 a submarine 90 using a tow cable 92 totow an optical hydrophone sonar array 100. The hydrophone array 100 is alinear array of modules 102 connected end-to-end. Intermodule mechanicalconnectors 104 fasten the modules 102 together and to the tow cable 92.A ship could also tow the array 100. The modules 102 may range in lengthfrom 50 feet to over 250 feet, and arrays 100 are commonly severalhundred to several thousand feet in length.

A module 102, shown in FIG. 2, comprises at a forward end 106 a fibersplice tray 108, a female bulkhead coupling 110 that is part of theintermodule mechanical connector 104 shown in FIG. 1, a clevis 112,woven fiber protection cable assembly 114, and a fiber transitionsegment 116, then a hydrophone assembly 118, and at the aft end 120 afiber transition segment 116, a woven fiber protection cable assembly114, a clevis 112, and a male bulkhead coupling 121 that with theadjacent female bulkhead coupling 110 comprises the intermodulemechanical connector 104. The male bulkhead coupling 121 may be designedby one of ordinary skill in the art to mate with a female coupling.Optical sensing fiber 124, shown in FIG. 2 within tubing, spans thelength of the module. The module 102 is surrounded by a hollowcylindrical open pore polyurethane foam 126, split longitudinally toallow it to be placed around the hydrophone assembly 118. Gabardineweave polyester cloth may be used with adhesive tape to connect adjacentportions of foam. FIG. 3 shows a hydrophone assembly 118 with twohydrophone segments 128. The two hydrophone segments 128 each comprisean air-backed plastic mandrel 136 and semi-circular steel cages 130, 132that encapsulate and protect the mandrels 136 (one is removed to exposethe mandrel 136). Interconnect springs 134 connect hydrophone segments128.

The air-backed plastic mandrels 136 are acoustically sensitive hollowcylinders that may be fabricated from a polycarbonate resin such asLEXANÂ®104 (LEXAN is a registered trademark of General ElectricPlastics). In one embodiment, the mandrels 136 have a ⅜-inch outsidediameter and are approximately 4.5 inches long. The mandrels 136 areplugged at each end (plugs not visible) with plugs made of the samematerial as the mandrel 136, solvent bonded to the mandrel 136. Theoptical fiber may be a low bend loss single mode fiber.

The perforated steel cage halves 130, 132 surround and protect themandrels 136. The steel cage halves 130, 132 may be fabricated from 40percent open, 18 or 20 gauge, staggered perforated low carbon steelsheet.

Some of the steel cage halves 130 are slotted 131, while other steelcage halves 132 are not slotted. Slotted cage halves are placed at theforward, mid and aftmost channels of the hydrophone assembly 118 toallow use of tape at those locations or at any desired interval asdeemed appropriate by one skilled in the art.

The plastic interconnect spring 134 (FIG. 4) connecting the mandrels mayalso be the same material type as the mandrels 136. Solvent bonding isused to connect the mandrels 136 and springs 134. The interconnectsprings 134 mechanically separate the individual mandrels 136, providingpoints of flexure for the assembly 118, and facilitate the handling oflong continuous hydrophone assembly lengths. Optical fiber is receivedin a groove 135 in the interconnect springs 134 to transition the opticfiber from one mandrel 136 to the next. The pitch and dimension of thehelical void 137 may be as selected by one of ordinary skill in the art.

Several additional components of the module appear in FIGS. 5 and 6. Theair-backed mandrel 136 inside surface 138 defines a cylindrical voidterminated at each end of the mandrel with a plug 140. An internalstrength member assembly is designed to carry the load applied to themodule 102 and comprises an internal strength member 141. The internalstrength member 141 is a woven member of aramid fibers that surroundsthe hydrophone assembly 118 and is attached to each clevis 112 andincludes two positioning tapes 142, 143. Certain components of thehydrophone assembly 118 are fastened to the two positioning tapes 142,143 within the internal strength member 141 in order to maintain theirrelative positions, including the foam 126 with polyester thread 145. InFIG. 5 the optical sensing fiber 124 is only shown in tubing; no baresensing fiber is shown.

A bypass cable assembly comprises additional jacketed optical fibers,which are bypass fibers 144, attached to a woven cable 146. The wovenbypass cable 146 carries the bypass fibers 144 to aft modules bytransitioning the fibers from the forward woven fiber protection cableassembly 114, around the hydrophone assembly 118 outside of the foam126, to the aft woven fiber protection cable assembly 114. A hose 148 ispulled over the entire assembly and fastened to the female bulkheadcoupling 110 and male bulkhead coupling 121 (FIG. 2) at each end. Atermination assembly 150 resides within the bulkhead couplings 110, 121.

The fiber transition segment 116 and the woven fiber protection cableassembly 114 are integrated as shown in FIG. 7 for use in the presentinvention. Together these elements protect the optical sensing fiber asit transitions between the central axis of the module 102 and thehydrophone assembly 118 at both ends of the module.

The woven fiber protection cable assembly 114 is shown in FIGS. 8, 9,and 10. The woven fiber protection cable assembly 114 includes a wovenfiber protection cable 170 and etched polytetraflouroethylene (PTFE,such as TEFLONÂ®; TEFLON is a registered trademark of the DuPontCorporation) tubing 172, 174. One tube 172 contains the optical sensingfiber and the other tube 174 contains bypass fibers (described below).The woven cable 170 is an elastic member comprising a plurality ofparallel elastic strands knitted together. The elastic member isfabricated from parallel strands of elastane (spandex) elastic fibers(such as LYCRAÂ®; LYCRA is a registered trademark of the DuPontCorporation). A single ply polyester yarn is utilized to knit theelastic strands together. The ultimate elongation of the woven elasticis specified to be a minimum of 50 percent. The cable 170 may beapproximately 0.50-inches wide.

The tubing 172, 174 may be, for example, either 21 or 22 gauge. Thetubing 172, 174 is installed in the cable 170 using a sinusoidalintegration scheme. At one end the woven cable 170 is configured to havea loop 176, and at the other end the two ends 178 of the cable 170 areinitially free and extend to either side of the fiber transition segment(not shown). The middle portion 180 of the cable 170 has three layers, acenter layer 182 and two outside layers 184, 186. The tubing 172, 174 isinserted between the center layer and outer layers 184, 186 in asinusoidal pattern with a period of 0.50 to 0.55 inches. The tubing 172,174 extends over the edges of the cable by approximately 0.05 inches.The end of the tubing 172 proximate to the fiber transition segment 116is formed into a retractable coil. This design provides protection tothe fiber 124 along with the ability to elongate and retract duringvariations in speed of the tow vessel. A length of optical fiber 124 isinstalled within the coiled tubing 172 for containment, protection andsubsequent splicing with the hydrophone assembly 118.

The woven fiber protection cable assembly 114 may be made by folding alength of cable in half, making a loop 176 at the folded end, insertingthe center layer 182 in the middle section 180, and separating the freeends 178 that go around the fiber transition segment 116. The outsidelayers 184, 186 of the cable 170 are sewn to the center layer 182 alongeach side, using two-ply textured polyester yarn.

The woven fiber protection cable assembly 114 provides a means fortransitioning optical fibers from the optical hydrophone assembly 118and bypass fiber cable (described below) assemblies to the bulkheads(for example, see forward bulkhead 110 in FIG. 5), which allowsintermodule connectivity. The fiber is protected from the point at whichit transitions from the hydrophone assembly 118 where the fiber startsinto or exits its helical pitch, a point where the fiber would otherwisebe susceptible to breakage, to the central axis of the module assembly102 and into and through the module bulkhead coupling 110, and clevis112. The woven fiber protection cable assembly 114 also provides thenecessary capability to elongate and retract during variations of towspeed induced drag loading without imparting strain on the fiber.

The fiber transition segment 116, shown in FIGS. 7, 11 and 12,transitions the optical sensing fiber 124 between the central axis ofthe module 102 and the hydrophone assembly 118, and is mounted tointerconnect springs 134 at both the forward 106 and aft 120 ends of thehydrophone assembly, as shown in FIG. 2. The transition segment 116 hasan internal groove 190 that is aligned with and has approximately thesame pitch as the interconnect spring groove 135 (FIG. 4). The fibertransition segment conical portion 192 is molded around an insert 194that is the same material as the interconnect spring 134. The insert 194is solvent bonded to the interconnect spring 134 thereby connecting thefiber transition segments 116 to the end of the hydrophone assembly 118for transitioning the optical sensing fiber 124 from the hydrophoneassembly 118.

The transition segment 116 functions as bend strain relief to provide asmooth transition for the fiber 124 across the edge face of thecylindrical mandrel 136 and interconnect spring 134. Mathematicallymodeling the transition segment 116 as a bend strain relief as known byone of ordinary skill in the art may be performed to define the materialproperties (i.e., elastic modulus) and shape of the transition segment116 given the root diameter at its base 196, minimum bend radius, andthe fiber diameter. Given a root diameter of 0.5 inches, for oneembodiment a material with an elastic modulus of 8,400 psi was required.The 0.5-inch root diameter was required in order to provide a smoothtransition from the interconnect spring 134 to the transition segment116. The smaller end 198 of one embodiment of the transition segment 116has a 0.312-inch diameter, with an end rounded at a 0.16-inch radius.The conical portion 192 of this transition segment 116 is 3.5 incheslong. A 90-A durometer polyurethane may be used for fabrication due toits molding characteristics and its compatibility with the module fillfluid, and may be molded around a LEXANÂ® 104 insert 194 to allowsolvent bonding to the adjacent interconnect spring 134. The portion ofthe insert 194 that extends from the conical portion 192 of thetransition segment 116 has an outside diameter that matches the insidediameter of the interconnect spring 134.

The transition segment 11 6 interfaces with the interconnect spring 134affixed to the last hydrophone mandrel at each end of the hydrophoneassembly 118. The groove 135 in the spring 134 on the last mandrel ateach end of the hydrophone assembly 118 is aligned with the groove 190in the transition segment 116 and solvent bonded. The hydrophone fiber(not shown) transitions from the last hydrophone mandrel by continuingthe spiral rotation of the fiber off of the interconnect spring 134 andonto the transition segment 116. The bare fiber is laid along thehelical groove 190 in the transition segment 116 for two to threerevolutions. The coiled portion of the optical sensing fiber tube 172 iswound into the grooves 190 of the transition segment 116 for two tothree revolutions. The fiber then transitions into the protective tube172. The tube 172 continues along the helical groove 190 for two tothree additional revolutions. Both the bare fiber and the etched PTFEtube 172 are bonded in the groove 190. The tubing 172 exits out of themolded groove 190 into several (three to five) free retractable coils.The tube 172 with the optical sensing fiber inside is then integratedwith the woven fiber protection cable assembly 114. A service length ofoptical fiber is maintained in order to allow for splicing to theoptical hydrophone assembly 118.

The transition segment 116 provides a controlled means of graduallytransitioning the fiber to or from a wound helix to an otherwisestraight configuration. The fibers are protected within the tube 172, asthey exit the transition segment 116 and pass through the woven fiberprotection cable assembly 114 into the module bulkhead coupling 110 andclevis 112.

As shown in FIGS. 13 and 14, the bypass cable assembly 200 protectsoptical bypass fibers, and includes a jacketed bundle of bypass fibers144 attached to a woven cable 146. The bypass cable assembly 200provides the capability to transition any number of fibers 144 withinthe module 102 around the hydrophone assembly 118 to service aft modules102. The fibers 144 that service aft modules 102 must pass along sidethe preceding optical hydrophone assembly 118 without being damaged. Thebypass cable assembly 200 provides a protected and reliable means oftransitioning a bundle of optical fibers 144 from the forward mostbulkhead coupling 110 to the aft most clevis 112 within a module 102.This design component also provides the necessary capability to elongateand retract during variations of tow speed induced-drag loading withoutimparting strain on the fiber.

Bypass fibers run parallel to the hydrophone assembly to serve as theactive-sensing fiber for subsequent and discrete blocks of additionalhydrophone channels in aft modules. A number of individual bypass fibersare packaged into the single jacketed bundle 144, with the jacket in oneembodiment being made of a thermoplastic polyether elastomer (such asHYTRELÂ®; HYTREL is a registered trademark of the DuPont Corporation),with an integrated strength member made of para-aramid fiber producedfrom poly-paraphenylene terephthalamide (such as KEVLARÂ®; KEVLAR is aregistered trademark of the DuPont Corporation). This package of bundledfibers 144 is attached in a sinusoidal attachment integration scheme tothe woven cable 146 that spans the entire length of the module 102. Inone embodiment, the bundled bypass fibers 144 are also attached to thewoven fiber protection cable 114, and because the bypass fibers 144 arealready jacketed, the PTFE tubing used on the optical sensing fiber 124along the woven fiber protection cable 114 is not needed on the bypassfibers 144. The bypass cable 146 is woven from 15 parallel strands ofelastane (LYCRAÂ® elastic) having a diameter of 0.012 inches. A singleply polyester yarn is utilized to knit the elastic strands together. Twostrands of single ply liquid crystal polymer thermoplastic multifilamentfiber (such as VECTRANÂ®; VECTRAN is a registered trademark of HoechstCelanese Corporation) are woven into the cable 146 along the borders toestablish the ultimate elongation of the woven cable 146, which is aminimum of 10 percent. These features provide the necessary elongationcharacteristics so that the bypass fibers 144 are not strained or brokenas a result of towing at high speed.

The two positioning tapes 142, 143 of the internal strength memberassembly run the length of the module and are attached to devises 112 ateach end. In one embodiment the tapes are 0.5-inch wide and are made ofa synthetic thermoplastic, such as nylon. The woven cable 146 with itsintegrated fiber bundle 144 is stitched with yarn that is two-ply,textured polyester yarn along one of the elastic component positioningtapes 143 every 12 inches, sandwiching the fiber bundle 144 between thewoven cable 146 and the positioning tape 143. This method of attachmentprotects the fiber bundle 144. The cable 146 is left unattached nearboth ends to allow it to transition into the woven fiber protectioncable assemblies 114.

FIG. 15 shows a fiber-optic splice tray 108 and termination assembly 150in their positions relative to the intermodule female bulkhead coupling110, clevis 112, woven fiber protection cable assembly 114, and fibertransition segment 116 at the aft end 120 of a module 102. A similarconfiguration exists at the forward end 106 of a module 102.

The termination assembly 150 comprises a module oil seal assembly 202and a fiber seal assembly 203. The module oil seal assembly 202 is shownin FIGS. 16 through 18. The module oil seal assembly 202 is the primaryhydrostatic seal for the module fill fluid, and comprises a cylinder 204with one end open that has a circumferential ring 206 and the other endsubstantially closed. The module oil seal assembly 202 has a centrallylocated orifice 208 in the substantially closed end of the cylinder thataccepts a threaded check valve 212 and seal screw 210. The cavity 214defined by the cylinder 204 also accommodates a self-retracting coiledtube 216. The module oil seal assembly 202 also provides a threadedtermination point 217 for the adjacent end of the woven fiber protectioncable assembly 114, using a fastener such as a machine screw 219.O-rings 220, 222, 224 provide seals between mating parts. O-rings 226 onthe outside of the bulkhead coupling 110 provide a seal between thebulkhead coupling 110 and the hose (not shown).

The female bulkhead coupling 110 has alignment pins 229 (two of threeare shown) to facilitate mating with an adjacent male coupling 121 (FIG.2). A port 231 for an additional threaded check valve assembly is alsoprovided.

A static seal is formed at the interface of the intermodule bulkheadcoupling 110 and clevis 112 by threading the coupling 110 onto theclevis 112, which compresses the O-ring 220 between the module oil sealring 206 and the internal face of the coupling 227, and alsomechanically restrains the module oil seal assembly in position. Sealantmay be used as an alternative to an O-ring as known by one of ordinaryskill in the art. The module oil seal assembly 202 also provides twoidentical counter-bored cavities 228 with O-ring sealing surfaces, whichaccept optical fiber seals 230 equipped with radial O-rings 232 forstatic sealing. The walls of the counter-bored holes 228 are machined tobe radial sealing surfaces for the O-rings 232.The threaded check valve212 permits the injection or removal of module fill fluid on anindividual module basis. Both sensing and bypass optical fibers residein the self-retracting coiled tube 216, which when mated to the fibersplice tray 108 provides means for managing the excess optical fiberservice length required for accessing the fibers within the fiber splicetray 108. Extension and retraction of the coiled tube 216 can beaccomplished without imparting strain on the optical fibers. The formed,self-retracting coiled tube 216 maintains a constant radius for thefibers residing within, thus preventing damage resulting from violationsof the fibers” minimum bend radius.

The module oil seal design accommodates the optical fiber seal assembly203, shown together in FIG. 18. Bare optical fibers 124, 233 passthrough a fiber seal retainer 234 (FIGS. 19 and 20) and the fiber seal230 (FIGS. 21 and 22). The inner cavity of the fiber seal 230 is thenback filled with an epoxy potting compound, which is compatible with themodule fill fluid. The potting compound forms a reliable hydrostaticseal between the fibers 124, 233 and the metallic casing of the seal230. A radial O-ring 232 is installed onto the fiber seal 230 and thepotted seal is inserted into the counter-bored cavity 228 of the moduleoil seal cylinder 204. The fiber seal retainer 234 is threaded into themodule seal cylinder 204 in order to secure the fiber seal 230 in place.The etched PTFE tubes 172, 174 (only 172 is shown) extending from thewoven fiber protection cable assembly 114 are installed over tubes 238in the fiber seal retainer 234 and secured with the compressive tubestops 240 (only one shown in FIG. 18; FIGS. 23 and 24). Retainer caps242 (FIG. 25) are threaded over the tube stops 240 onto the fiber sealretainer 234 to ensure that the PTFE tubes 172, 174 are securely held inplace. After this procedure has been completed, the coupling 110 isthreaded onto the clevis 112 forming the module seal as described above.This establishes a reliable hydrostatic seal, which in one fabricatedembodiment was demonstrated to withstand pressures in excess of 3,000psi.

The termination assembly 202 is a protected means for providinghydrostatic module and optical fiber seals at the forward and aftbulkhead couplings 110 (aft bulkhead coupling is not shown) within amodule 102. They also provide the capability to inject fill fluid to orremove fill fluid from each discrete module 102 prior to integrationinto a full towed acoustic array module string. These attributes are aprerequisite for making each module 102 a stand-alone entity that can befabricated, optically tested and oil filled for neutral buoyancy. Theincorporation of these components into the overall system design permitsinterchangeability between and within towed sonar acoustic arrays.

The integrity of the optical fiber is maintained (i.e., no inducedstrain or violation of minimum bend radius) within the seal assembly dueto the fact that the fiber is fully protected over its entire transitionlength through the seal. The self-retracting coiled tube 216 locatedwithin the module seal cylinder 204 provides a controlled method oftransitioning the optical fibers from the fiber seal assembly 203 to thefiber splice tray 108. The coiled tube 216 also provides flexibility(i.e. service length) to permit the removal and re-insertion of thefiber tray 108 to support the requirements of module interchangeabilityand array re-configuration.

The miniature fiber-optic splice tray assembly 108 for use in ahydrophone module 102 according to the present invention is shown inFIGS. 26 to 30. The fiber splice tray 108 houses spliced fibers at theconnection between modules 102. The fiber tray 108 has both entry andexit points 250 for the fiber at either end of the tray 108. Two pairsof entry and exit points 250 are provided in the event that one pair isinadequate to accommodate the fibers in use. The bottom section 252 ofthe tray 108 mates with the top section 254, and an internal groove 256in the bottom section is of sufficient depth to accommodate severalmeters of fiber in order to provide adequate service length forperforming fusion splices during initial assembly or subsequent repairoperations.

Each splice is surrounded by a rigid fusion splice sleeve that acts as asplint to protect the fiber at and adjacent to the splice. The rigidsleeve bends very little, and because of the miniature size of the tray,cannot accommodate the tight radii of the bends in the internal groove256. Therefore, the sleeve must be located within a straight section ofthe internal groove 256. A means of manipulating the rigid fusion splicesleeve to a position within the straight sections is required. Theinternal groove 256 is designed with multiple alternative fiber paths.In one embodiment, shown in FIGS. 26 through 29, the fiber tray 108 hastwo alternative paths 258, 260 at each end of the tray 108 and has anadditional two paths 262, 264 that cross in the middle of the tray asalternatives to the two parallel straight sections 266, 268. In anotherembodiment shown in FIG. 30, the tray 108 a bottom section 252 a hasonly two alternative paths at each end 258, 260. The fiber may be woundwithin the groove 256 (not shown), selecting the paths as required toplace the sleeve in a straight section 266, 268 of the groove 256. Themating top 254 for the tray 108, 108 a ensures that the fiber is totallyencapsulated or captured for further protection during any assembly orrepair operation. The tray 108, 108 a may be fabricated from, forexample, ASTM A276 stainless steel rod, and has a diameter of between0.608 and 0.612 inches. The radii of the arcs at each end may be on theorder of 0.3 inches or less.

An advantage of the fiber-optic splice tray 108, 108 a is that it canhouse fusion-spliced fibers, protective splice sleeves, and excess fiberservice length in a small physical space envelope. The tray 108, 108 aprovides access to the optical fibers as they transition between modules102 and serves as a protective housing for those components. Theminiature splice tray 108, 108 a accomplishes this within the bore ofthe thin-line towed sonar array intermodule coupling, thus providing aneffective means of enabling and managing fusion-spliced fibers within atightly confined volume. The small size of the splice tray 108, 108 a iscompatible with the physical geometry of existing towed array mechanicalconnectors and thus maintains commonality with existing handling systemrequirements, notably overall rigid length. A threaded boss 270 isprovided at each end of the tray 108, 108 a and is used as a temporaryattachment point for a housing/booting fixture to maintain the splicetray in a fixed relative position during hosing of the module 102. Thethreaded boss 270 can also accept a plunger that opens the check valve212 when the tray 108, 108 a is inserted into the bulkhead couplingduring mating of hydrophone modules 102.

An apparatus to allow splicing of a fiber across a mandrel is depictedin FIGS. 31 through 38. Short optical end terminations, referred to asfiber pigtails 278, remain after transitioning active sensing hydrophonefiber 124 into and through the intermodule mechanical connector 104.These fiber ends 278 must be spliced to the active sensing fiber 124 ofthe hydrophone assembly 118. The fiber splicing assembly comprises amandrel body 136, a splice protector 280, a splinted fusion splicesleeve 281, and rotation sleeves 282. The splice sleeve is utilized toprotect the fiber splice from the optical hydrophone assembly 118 andthe woven fiber protection cable assembly 114. The splice sleeve may bepolyvinylidene flouride (PVDF) heat shrinkable tubing with an interiorcoating of thermoplastic adhesive that is reinforced with a brass rodthat minimizes bending. In one embodiment, the splice sleeve isapproximately 0.9-long and is slid over the fiber just prior to makingthe splice. The splice protector 280 provides a recessed cavity 284 forsupporting and protecting the splinted fusion splice sleeve. Therotation sleeves 282 facilitate the winding of excess fiber required forthe fusion splicing operation down onto the mandrel body 136.

The fiber splice components 280, 282 are typically installed after thewoven fiber protection cable assemblies 114 are secured in the module102. The fiber pigtails 278 from the woven fiber protection cableassemblies 114 are fusion spliced with fiber pigtails 278 from thehydrophone assembly 118. The splice protector 280 is then bonded to thelast hydrophone mandrel at each end of the hydrophone assembly 118. Thesplinted protection sleeve is installed and shrunk with the applicationof heat over the splice and then secured within the recessed cavity 284on the splice protector 280. The two rotation sleeves 282 are utilizedto wind the excess service length of the fiber down onto the hydrophonemandrel 136 on both sides of the splice protector 280, and the fiber isplaced in the groove 285 in the rotation sleeves. The rotation sleeves282 are then bonded in place. Although the rotation sleeves are shownaligned with the splice protector 280 and with each other in FIG. 32,this may not necessarily be the case. The orientation of each rotationsleeve 282 on the mandrel 136 is determined by the length of the sensingfiber 124 on the respective side of the splice protector 280.

This splicing apparatus and methodology facilitate fusion splicetechniques within an optical hydrophone assembly. The new fiber spliceapparatus and method provide the capability to cost effectivelyfabricate sub-components of hydrophone assemblies off-line for laterintegration into a towed array optical module subassembly. The presentinvention also provides repair capability in the event of a fiber breakduring fabrication of the optical hydrophone assembly. The splicecomponents allow control of the placement, as well as protection of, thefusion splice sleeve on the optical hydrophone mandrel. The fiber spliceof the present invention provides a controlled geometry that allows safehandling and permanent protection of the optical fiber.

There is a reduction in risk of fiber breakage resulting from having totransition the active sensing fiber from the hydrophone assembly intoand through the module bulkhead couplings. The splicing technique of thepresent invention provides the capability to transition an autonomousfiber, which has been integrated into the optical end terminationassembly off-line, into and through the module bulkhead couplings. Thisembodiment of the invention eliminates the potential of sacrificing anentire hydrophone assembly due to one fiber break during the fabricationof the module subassembly. Another major attribute is the ability toreside within the existing physical envelope of optical hydrophoneassemblies with minimal impact to the overall sensitivity of the system,enabling intermodule connectivity using low loss optical fiber fusionsplicing techniques.

The fabrication process of one embodiment of a module begins with theassembly of the hydrophone 118. The mandrels 136, plugs 140, andinterconnect springs 134 are assembled, and the optical sensing fiber124 is wound on these components (FIGS. 2-6). The steel cage halves 130,132 are added. A 0.5-inch wide woven polyester tape 137 is wrappedaround and adhesively bonded to the steel cage 130, 132 and throughperiodically spaced pairs of slots 131 (FIG. 13). Utilizing 1.5-inchwide strips of polyester cloth, to which a thermoplastic adhesive isapplied, individual foam sections four feet in length are joinedtogether to form a continuous length of hollow open pore foam 126.Before the foam assembly 126 is installed, the internal strength member141 (ISM) along with positioning tapes 142, 143 are placed under aninitial tension to insure that its length is equivalent to the nominalhose length. Then the foam assembly 126 is installed. Next, at thecenter of the ISM 141, the foam assembly 126 is secured to both of theinternal positioning tapes 142, 143 every 18 inches using polyesterthread 145 as depicted in FIG. 39 (only one side of the foam and onepositioning tape shown). The entire length of the stitching is between1.2 and 1.5 inches.

The next step in the fabrication process is the installation of thebypass cable assembly 200 that comprises the jacketed bypass fibers 144and woven fiber bypass cable 146. The bypass cable 146 is stitched every12 inches along the positioning tape 143, as depicted in FIG. 40, sothat the jacketed bypass fibers 144 are sandwiched between the wovencable 146 and the positioning tape 143. The stitching 288 is a loopstitch of polyester thread with two or three loops. This method ofattachment provides increased protection for the fiber bundle. The cableis left unattached near both ends so that it may be transitioned intothe fiber protection components.

The ISM 141 and its positioning tapes 142, 143 are then placed underadditional tension in order to elongate it in preparation for theinstallation of the hydrophone assembly 118 and other components up tothe devises 112. The length of the ISM 141 for the installation of thehydrophone assembly is based upon several factors: nominal hose length,hose elongation characteristics, number and design of interconnectsprings.

Elongating the ISM prior to installation of the hydrophone assembly wasfound in testing a prototype to help optimize the interconnect springgap spacings under operational tow speeds and during reeling. Adherenceto this installation methodology allows full extension of the hydrophoneassembly 118 during maximum elongation of the module 112, which occursat peak tow speeds.

The hydrophone assembly 118 is attached to both positioning tapes 142,143 by passing 0.5-inch wide woven polyester tape 137 (FIG. 41) throughand around the slotted cage halves 130 and sewing the free ends to thetape 142, 143 through the foam 126. As previously noted, slotted cagehalves may be placed at the forward, mid, and aftmost channels of thehydrophone assembly, or at any desired interval. This technique is usedto provide a loosely coupled attachment system. In order to provideenhanced positional stability, each hydrophone 118 element is bonded tothe open pore foam 126 using a thermoplastic adhesive. The adhesive bondis formed between the foam 126 and the 0.5-inch wide strip of wovenpolyester tape 137 that has been wrapped around and adhesive bonded toeach set of cage halves 130.

The next step in the fabrication process is the integration of the fibertransition segment 116 with the woven fiber protection cable assembly114 and the interconnect spring 134 in order to construct the fiberprotection assembly for both the forward and aft ends of the module(FIGS. 7-12). This step may be performed at any time during fabricationsince the intent is to fabricate this assembly off-line. The transitionsegment 11 6, which has an internal groove with the same pitch as aninterconnect spring 134, is aligned with a spring 134 and solventbonded. This attachment scheme is identical to the attachment methodutilized for attaching the hydrophone mandrels 136 to the interconnectsprings 134. The retractable coiled tube 172 extending from the wovenfiber protection cable assembly 114 is wound into the grooves 190 of thetransition segment 11 6 for two to three revolutions. The bare fiberexiting from within the tube continues along the helical groove 190 fortwo to three additional revolutions. Both the bare fiber and etched PTFEtube 172 are secured within the groove 190 with ultraviolet curableoptical adhesive such as Norland NOA UV curable adhesive available fromNorland Products, Inc. of New Brunswick, N.J. The helical winding of theoptical fiber is continued as it transitions off of the transitionsegment 116 and onto the interconnect spring 134. A service length ofoptical fiber is maintained (approximately one meter) in order to allowfuture fusion splicing of the optical fiber to the optical fiber on thehydrophone assembly 118.

The woven fiber protection cable assembly 114 is secured within themodule 102 by stitching one of the two reinforced branches 178 of thewoven cable 170 to the internal positioning tape 142 and the otherbranch 178 to the other positioning tape 143. The bypass fiber 144 istransitioned from the woven cable 146 to the woven fiber protectioncable assembly 114 by maintaining its sinusoidal pattern along one ofthe branches 178 of the woven fiber protection cable 170. The jacketedfiber bundle 144 is then transitioned off of the woven fiber bypasscable branch 178 and may enter a separate protective carrier 174 (i.e.,PTFE tubing) that is integrated within the woven fiber protection cable170, or in the preferred embodiment the jacketed fiber bundle 144 isdirectly integrated into the woven fiber protection cable 170. The fiberprotection cable 170 is then inserted through the clevis 112 andbulkhead 110. This design approach ensures the survivability of both theactive hydrophone sensing fiber and bypass fibers in this critical areawhere they are transitioned to the central axis of the module 102. Italso provides the desired characteristics for elongation and retraction.

After the forward and aft woven fiber protection cable branches 178 aresecured within the module 102, the fiber pigtails from the transitionsegments 116 are fusion spliced with the fiber pigtails of thehydrophone assembly 118. The splice protector 280 is bonded to the lasthydrophone mandrel 136 at each end of the hydrophone assembly 118. Acustom designed splinted protection sleeve is installed over the spliceand then secured within the recessed cavity 284 on the splice protector280. Two rotation sleeves 282 are utilized to wind the excess servicelength of fiber down onto the hydrophone mandrel 136 on both sides ofthe splice protector 280. The two rotation sleeves 282 are bonded inplace resulting in the final configuration that is depicted in FIG. 32.This mandrel 136 is intentionally breached to allow it to free flood inorder to make it acoustically insensitive. The cage halves 130 and 132are then placed around the mandrel body 136 and bonded in place in thesame manner as all other hydrophone mandrels.

The woven fiber protection cables assemblies 114 are attached to themodule oil seal 202 as shown in FIGS. 15 and 16. The fiber protection isattached to the module oil seal 202 with a machine screw 219 and thetray 108 is coupled to the seal via the coiled tubing 216 through whichthe fibers transition. At this point the fibers (hydrophone and bypass)are transitioned out of the woven cable assembly 170 and into the tubes238 of the fiber seal retainer 234, through the coiled tube 216 and intothe fiber tray 108. The PTFE tubes 172, 174 for the fiber are terminatedat the fiber seal 203 (FIG. 18). The woven fiber protection cableassembly 170 is attached to the module oil seal 202 with a fastener,preferably a machine screw 219 (FIG. 16) that ensures that all loads arecarried by the woven cable with none being transferred to the protectivecarrier or fiber. A sufficient length of bare fiber is wound and storedinto the internal groove 256 within the fiber tray 108 in order toprovide the service length required for performing fusion splices forintermodule connectivity.

In order to accommodate the hosing process, where the hose is slid overthe module 102, the forward end of the module 102 is terminated with atermination assembly 150, a fiber splice tray 108 and a forward bulkheadcoupling 110. The aft end is terminated with a termination assembly 150,a temporary fiber splice tray 108, and temporary tooling. The aft endthat is not fully terminated has temporary tooling installed on it untilthe hose is slid over the module. For hosing, the aft end of the ISM 141must be pulled into and through the hose 148. Temporary tooling 300,shown in FIGS. 42 and 43, is designed to secure the aft fiber splicetray 108 and coiled tubing 216 within a protective enclosure 302 that issized to fit within the hose. The temporary tooling 300 comprises theprotective enclosure 302, a pulling adapter 310, and an eyebolt 312. Theclevis 112 is part of the ISM 141 and has threads that mate with theprotective enclosure 302. The protective enclosure houses the aft fibersplice tray 108, 108 a and secures it to inhibit rotational orextensional movement during the hosing/booting process. The pullingadapter serves as an interface between the enclosure 302 and the eyebolt312. It is tapered to accommodate a lead in for smooth entry into thehose. The eyebolt 312 provides for easy attachment to the wire rope thatis used to pull 314 the module 102 into the hose 148.

A wire rope is passed through the hose and attached to a swivel and thenthe eyebolt 312 on temporary tooling 300 at the aft end of the ISM 141.The hose 148 is tensioned and the ISM 141, with the hydrophone assembly118 installed, is pulled into the hose. The temporary tooling 300 isthen removed and the remaining module 102 end component is installed,comprising the aft bulkhead coupling 110 as depicted in FIG. 15. Themodule 102 is then oil filled to complete the assembly process. Theembodiments of the present invention protect the active sensing opticalfiber and the bypass fiber from damage that could otherwise result inthe normal course of towing and handling optical hydrophone sonararrays. The effect of elongation and bending requirements imposed on themodule are reduced on the optical fiber by the present inventionembodiments, which result in a durable and reliable optical hydrophonesonar array. The embodiments of the present invention also facilitatethe assembly of the arrays, in that modules may be individuallyconstructed. Subassemblies within the module, such as the hydrophoneassembly and the parts of the module from the fiber transition segmentto the adjacent end of the module, may be fabricated independently andthen combined.

Although the present invention has been shown and described inconsiderable detail with respect to only one exemplary embodiment foreach component, it should be understood by those skilled in the art thatwe do not intend to limit the invention to the one embodiment sincevarious modifications, omissions and additions may be made to thedisclosed embodiment without materially departing from the novelteachings and advantages of the invention, particularly in light of theforegoing teachings. For example, the components may be of modifiedshapes and sizes. Accordingly, we intend to cover all suchmodifications, omission, additions and equivalents as may be includedwithin the spirit and scope of the invention as defined by the followingclaims. In the claims, means-plus-function clauses are intended to coverthe structures described herein as performing the recited function andnot only structural equivalents but also equivalent structures. Thus,although a nail and a screw may not be structural equivalents in that anail employs a cylindrical surface to secure wooden parts together,whereas a screw employs a helical surface, in the environment offastening wooden parts, a nail and a screw may be equivalent structures.

1. A mount for use in an optical fiber hydrophone module, the modulecomprising an optical hydrophone core, the hydrophone core beinggenerally cylindrical in cross-section, having a longitudinal axis, andcomprising a plurality of mandrels helically wrapped with optical fiberand connected in linear relation with interconnect springs, the mountcomprising: a cylindrical metal cage encircling the hydrophone core,circumferentially abutting the interconnect springs; cloth tape wrappedaround and affixed to the metal cage; an open pore foam encircling andcircumferentially abutting the metal cage; means for attaching the foamto the cloth tape; an internal strength member encircling the foam,comprising a hollow woven cylinder and at least one longitudinalpositioning tape that extends inside the cylinder for the full length ofthe cylinder and is fastened to the cylinder at each end; and means forfastening the positioning tapes to the foam at spaced intervals alongthe axis.
 2. A mount for use in an optical fiber hydrophone module asrecited in claim 1, wherein the metal cage is steel.
 3. A mount for usein an optical fiber hydrophone module as recited in claim 1, wherein thecloth tape is woven polyester.
 4. A mount for use in an optical fiberhydrophone module as recited in claim 1, wherein the open pore foam ispolyurethane.
 5. A mount for use in an optical fiber hydrophone moduleas recited in claim 1, wherein the means for attaching the foam to thecloth tape is thermoplastic adhesive.
 6. A mount for use in an opticalfiber hydrophone module as recited in claim 1, wherein the internalstrength member comprises aramid fibers.
 7. A mount for use in anoptical fiber hydrophone module as recited in claim 1, wherein the meansfor fastening the positioning tape to the foam comprises thread.
 8. Amount for use in an optical fiber hydrophone module as recited in claim7, wherein the thread is polyester thread.
 9. A mount for use in anoptical fiber hydrophone module as recited in claim 7, wherein thespaced intervals of fastening the positioning tape to the foam along theaxis are approximately 18 inches.
 10. A mount for use in an opticalfiber hydrophone module as recited in claim 9, wherein at each locationthe length of stitching along the axis is approximately from 1.2 to 1.5inches.
 11. A mount for use in an optical fiber hydrophone module, themodule comprising an optical hydrophone core, the hydrophone core beinggenerally cylindrical in cross-section, having a longitudinal axis, andcomprising a plurality of mandrels helically wrapped with optical fiberand connected in linear relation with interconnect springs, the mountcomprising: a cylindrical steel cage encircling the hydrophone core,circumferentially abutting the interconnect springs; woven polyestercloth tape, wrapped around and affixed to the steel cage; a polyurethaneopen pore foam encircling and circumferentially abutting the steel cage;thermoplastic adhesive for attaching the foam to the cloth tape; anaramid fiber internal strength member encircling the foam, comprising ahollow woven cylinder and at least one longitudinal positioning tapethat extends inside the cylinder for the full length of the cylinder andis fastened to the cylinder at each end; and polyester thread forfastening the positioning tape to the foam at spaced intervals along theaxis.
 12. An optical fiber hydrophone module, the module comprising: anoptical hydrophone core, the hydrophone core being generally cylindricalin cross-section, having a longitudinal axis, and comprising a pluralityof mandrels helically wrapped with optical fiber and connected in linearrelation with interconnect springs; a cylindrical metal cage encirclingthe hydrophone core, circumferentially abutting the interconnectsprings; cloth tape, wrapped around and affixed to the metal cage; anopen pore foam encircling and circumferentially abutting the metal cage;means for attaching the foam to the cloth tape; an internal strengthmember encircling the foam, comprising a hollow woven cylinder and atleast one longitudinal positioning tape that extends inside the cylinderfor the full length of the cylinder and is fastened to the cylinder ateach end; and means for fastening the positioning tape to the foam atspaced intervals along the axis.
 13. An optical fiber hydrophone moduleas recited in claim 12, wherein the cloth tape is woven polyester tape.14. An optical fiber hydrophone module as recited in claim 12, whereinthe open pore foam is polyurethane.
 15. An optical fiber hydrophonemodule as recited in claim 12, wherein the means for attaching the foamto the cloth tape is thermoplastic adhesive.
 16. An optical fiberhydrophone module as recited in claim 12, wherein the means forfastening the positioning tape to the foam comprises thread.
 17. Anoptical fiber hydrophone module as recited in claim 16, wherein thethread is polyester thread.
 18. An optical fiber hydrophone module asrecited in claim 16, wherein the spaced intervals of fastening thepositioning tape to the foam along the axis are approximately 18 inches.19. An optical fiber hydrophone module as recited in claim 18, whereinat each location the length of stitching along the axis is approximatelyfrom 1.2 to 1.5 inches.
 20. An optical fiber hydrophone module, themodule comprising: an optical hydrophone core, the hydrophone core beinggenerally cylindrical in cross-section, having a longitudinal axis, andcomprising a plurality of mandrels helically wrapped with optical fiberand connected in linear relation with interconnect springs; acylindrical steel cage encircling the hydrophone core, circumferentiallyabutting the interconnect springs; woven polyester cloth tape, wrappedaround and affixed to the steel cage; a polyurethane open pore foamencircling and circumferentially abutting the steel cage; thermoplasticadhesive for attaching the foam to the cloth tape; an aramid fiberinternal strength member encircling the foam, comprising a hollow wovencylinder inclusive and at least one longitudinal positioning tape thatextends inside the cylinder for the full length of the cylinder and isfastened to the cylinder at each end; and polyester thread for fasteningthe positioning tape to the foam at spaced intervals along the axis. 21.A mount for use in an optical fiber hydrophone module, the modulecomprising an optical hydrophone core, a cylindrical metal cage, an openpore foam, and an internal strength member, the hydrophone core beinggenerally cylindrical in cross-section, having a longitudinal axis, andcomprising a plurality of mandrels helically wrapped with optical fiberand connected in linear relation with interconnect springs, thecylindrical metal cage encircling the hydrophone core, circumferentiallyabutting the interconnect springs, the open pore foam encircling andcircumferentially abutting the metal cage, and the internal strengthmember encircling the foam, comprising a hollow woven cylinder and atleast one longitudinal positioning tape that extends inside the cylinderfor the full length of the cylinder and is fastened to the cylinder ateach end, the mount comprising: cloth tape wrapped around and affixed tothe metal cage; means for attaching the foam to the cloth tape; andmeans for fastening the positioning tape to the foam at spaced intervalsalong the axis.
 22. A mount for use in an optical fiber hydrophonemodule as recited in claim 21, wherein the means for attaching the foamto the cloth tape is thermoplastic adhesive.
 23. A mount for use in anoptical fiber hydrophone module as recited in claim 21, wherein themeans for fastening the positioning tape to the foam comprises thread.24. A method of mounting an optical fiber hydrophone, the hydrophonecomprising an optical hydrophone core, the hydrophone core beinggenerally cylindrical in cross-section, having a longitudinal axis, andcomprising a plurality of mandrels helically wrapped with optical fiberand connected in linear relation with interconnect springs, the mountcomprising: placing a cylindrical metal cage around the hydrophone core,the cage circumferentially abutting the interconnect springs; wrappingwoven polyester tape around and affixing the tape to the metal cage;placing an open pore foam around and circumferentially abutting themetal cage; attaching the foam to the cloth tape; placing an internalstrength member around the foam, comprising a hollow woven cylinderinclusive of aramid fibers and at least one longitudinal positioningtape that extends inside the cylinder for the full length of thecylinder and is fastened to the cylinder at each end; tensioning thepositioning tape; and fastening the positioning tape to the foam atspaced intervals along the axis.
 25. A method of mounting an opticalfiber hydrophone as recited in claim 24, wherein the cloth tape is wovenpolyester tape.
 26. A method of mounting an optical fiber hydrophone asrecited in claim 25, wherein the open pore foam is polyurethane.
 27. Amethod of mounting an optical fiber hydrophone as recited in claim 25,wherein the cloth tape is attached to the foam with a thermoplasticadhesive.
 28. A method of mounting an optical fiber hydrophone asrecited in claim 24, wherein the positioning tape is fastened to thefoam with thread.
 29. A method of mounting an optical fiber hydrophoneas recited in claim 28, wherein the thread is polyester thread.
 30. Amethod of mounting an optical fiber hydrophone as recited in claim 28,wherein the spaced intervals of fastening the positioning tape to thefoam along the axis are approximately 18 inches.
 31. A method ofmounting an optical fiber hydrophone as recited in claim 28, wherein ateach location the length of stitching along the axis is approximatelyfrom 1.2 to 1.5 inches.